Patent GB-483183-A (GB)
Title: Improvements in the method of, and apparatus for, producing toothed gear wheels
IPC: B23F9/08
Filed: 1937-03-23
Abstract: 483,183. Gear-cutting. KLINGELNBERG, G. A., KLINGELNBERG, W. H., and KLINGELNBERG, H. W., (trading as KLINGELNBERG SOHNE, W. F.). March 23, 1937, No. 8551. Convention date, March 25, 1936. [Class 83 (iii)] In generating bevel gears by means of worm hobs, the oscillatory generating motion of the tool around the basic crown gear axis is performed at non-uniform speed so as to secure better utilization of the cutting capacity of the hob. In cutting a bevel gear with a worm hob which is swung uniformly around the imaginary crown wheel axis the distribution of the cut is as shown in Fig. 1 wherefrom it appears that shortly after engaging the blank comparatively large cuts are taken which gradually decrease as the cutting proceeds. If the line 2 represents a generator of the hob lying in the crown wheel plane it is seen from Fig. 3 that a work piece having a generator 5 in the crown wheel plane is first engaged by the end 2<1> of the hob and that teeth spaced along the hob towards the end 2<11> come into action successively. The field of contact is indicated by the area 8. The teeth towards the end 2<11> of the hob do less cutting than the teeth near the end 2<1> since they operate on tooth spaces already partly formed. This difference is accentuated in the case of taper hobs since the hob teeth then describe a larger circle at the end 2<1> than at the end 2<11>. A diagram of the cuts taken by cutting teeth spaced along the hob is shown in Fig. 6. In order to take full advantage of the cutting efficiency of the tool the velocity of swing of the cutter around the crown wheel axis should vary as shown in the curve V<1>, Fig. 7. This is approximated according to the invention by varying the speed according to the straight line V<11>. It is also preferable, in conjunction with this accelerated feed to accelerate the hob rotation in a similar way so that the number of generating cuts is not unduly reduced during the later stages of the operation. In the case of taper hobs this acceleration serves to maintain the cutting velocity approximately constant throughout the length of the hob. In a machine embodiment, Figs. 9 and 10, the tool 12 is rotated, and the crown wheel movement imparted to the face plate 14 by means of a shaft 17 connected through belt gearing and a speed controller 16 with a driving motor 15. The driving shaft 19 carries conical discs 18 connected bv a belt 21 to similar discs on a shaft 20. In order to vary the speed a shaft 22 may be rotated to separate one pair of discs and bring together the other pair. To correlate the speed variation with the face plate movement a gear 25 on the face plate is connected through shaft 27, spiral gears 28 and change gears 24 to the shaft 22. The speed may also be varied by operating a hand wheel 11. The speed control is reset to its original position when the face plate is reversed. The return movement of the face plate may be at high speed. In a modification separate speed controls may be provided for the face plate movement and for the hob rotation. The invention is also applicable to cutting spur or helical gears by the method in which the hob is arranged on an inclined axis andis fed relatively past the blank in a tangential direction. In this case the gear 25 is replaced by a rack fixed to the work or tool table.